textproduct: Rapid City

KEY MESSAGES

- Widespread near critical fire wx conditions across northeastern WY into western and south central South Dakota this afternoon.

- Strong southwest winds will continue through the afternoon hours with gusts already hitting 60-70 mph in spots.

- The strong winds will shift to the northwest later this evening into the overnight hours and overspread the region with gusts of 75- 80+ mph possible across northwestern SD.

- Despite meager QPF, potential exists for for snow squalls over western SD later tonight into early Thursday morning.

DISCUSSION

(This Evening Through Wednesday) Issued at 119 PM MST Wed Dec 17 2025

Strong southwesterly winds have developed across northeastern Wyoming and western South Dakota. Gusty downslope winds continue across the eastern Black Hills and foothills with peak gusts of 55-65 mph this morning and early afternoon.

Confidence is increasing in a higher impact high wind event for northwestern South Dakota across the I-90 corridor in western South Dakota overnight tonight behind two fronts in quick succession. Forecast soundings continue to show well-mixed boundary layers, mixing down a core of 80-90kt winds atop the mixed layer. Hi-res models pick up on this as well, coupled with MOS guidance (old school!) showing sustained winds of 40-50+ knots across northwestern SD overnight. The ingredients are there: 3-6 mb pressure rises behind the first front this evening, 6-9+ mb pressure rises behind the second/arctic front late tonight, strong CAA/mechanical mixing of higher momentum air, and a core of 70-100 knot winds at ~800-700 mb. Consequently, have increased winds in this forecast package across the western SD plains tonight with maximum wind gusts ~75-80 mph, although potential exists for 80+ mph. Looking at it probabilistically, the NBM has prob of gusts >75 mph ~65-75%+ for most of western SD; the 12z HREF/REFS have a similarly high probability of gusts >75 mph overspreading NW SD after 11pm MT behind the second front, spreading southeastward through 6am. The strongest winds (70+ mph) are expected to stretch from NW SD into the foothills and along I-90 in western SD. Winds will diminish from west to east late Thursday morning through the afternoon hours.

Light rain will quickly transition to snow as the arctic front pushes into the NW SD later this evening. While the best moisture will remain displaced east, strong low-level lapse rates coupled with very strong winds will support snow squall potential in any heavier bands of snow overnight. The best snow squall potential will exist after 10pm across NW SD into the western SD plains through the overnight hours, although meager QPF/moisture will yield only transient visibility reductions.

Upper level flow will become zonal Friday with highs warming back into the 50s and 60s ahead of another clipper system Friday night into Saturday morning with light snow across NE WY into the Black Hills. Cooler Saturday behind another cold front before dry, zonal/southwesterly flow returns for next week - looking mild for Christmas.

AVIATION

(For the 18Z TAFS Through 18Z Thursday) Issued At 1034 AM MST Wed Dec 17 2025

Strong southwesterly winds will continue to develop across NE WY and far western SD. Gusts up to 35-45 knots will be possible, especially across NE WY. Then a vigorous cold front will cross the region this afternoon/evening, bringing very strong winds, with gusts to 60kt or even higher in some locations. A band of rain will cross the area today, changing to snow as the front passes late this afternoon. This could result in locally MVFR/IFR visibility and ceilings. Otherwise, mainly VFR ceilings are expected through the TAF period.

FIRE WEATHER

Issued At 119 PM MST Wed Dec 17 2025

Strong west-southwesterly winds and low relative humidity will support near-critical fire weather conditions. Winds continue to gust 40-60+ mph across portions of NW WY into southwestern and south- central SD this afternoon. While relative humidity won't meet the traditional critical value (<15%), RH ~25-30% this afternoon coupled with the strong winds will support near-critical conditions.

UNR WATCHES/WARNINGS/ADVISORIES

SD...High Wind Warning until 11 AM MST Thursday for SDZ001-002-012- 013-025-041-072-073-078. High Wind Warning from 10 PM MST /11 PM CST/ this evening to 1 PM MST /2 PM CST/ Thursday for SDZ014-026-030>032-042>044- 046-047-049-074>077. High Wind Warning until 8 AM MST Thursday for SDZ024-027>029. WY...High Wind Warning until 11 AM MST Thursday for WYZ059-060. High Wind Warning until 8 AM MST Thursday for WYZ057. High Wind Warning until 5 AM MST Thursday for WYZ054-056. High Wind Warning until 5 PM MST this afternoon for WYZ055-058.